System for measuring and recording the forces acting on airplane controls and the like



Dec. 22, 1953 w w, WOOD, JR ET AL 2,663,187

SYSTEM FOR MEASURING AND RECORDING THE FORCES ACTING ON AIRPLANE CONTROLS AND THE LIKE Filed D80. 26, 1950 4 Sheets-Sheet l INVENTORS W/zzM/n n4 14 00, we.

15.97586 zz/n flp 42/4? BY M/W Dec. 22, 1953 w. w. wooo, JR. ET AL 2,663,187

SYSTEM FOR MEASURING AND RECORDING THE FORCES ACTING ON AIRPLANE CONTROLS AND THE LIKE Filed Dec. 26, 1950 4 Sheets-Sheet 2 m% T0 W W 5 W w M5 W M my u W 4 Dec. 22, 1953 w. w. wooD, JRJ. ET AL SYSTEM FOR MEASU 2,663,187 RING AND RECORDING THE FORCES ACTING ON AIRPLANE CONTROLS AND THE LIKE 0 4 Sheets-Sheet 3 Filed Dec. 26, 195

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Dec. 22. 1953 w. w. wooo, JR.. ET AL 2,663,187

SYSTEM FOR MEASURING AND RECORDING THE FORCES ACTING ON AIRPLANE CONTROLS AND THE LIKE Filed D80. 26, 1950 4 Sheets-Sheet 4 2 J 4 N\Q V r W m M Nw u M W R H A mm \M 5th E E...

Patented Dec. 22, 1953 SYSTEM FOR MEASURING AND RECORDING THE FORCES ACTING ON AIRPLANE CON- TROLS AND THE LIKE William W. Wood, Jr., Fenton, and Lester E.

Lundquist, Jr., Binghamton, N. Y., assignors to the United States of America as represented by the Secretary of the Air Force Application December 26, 1950, Serial No. 202,614

5 Claims.

1 The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon.

' This invention relates to a system for measuring the forces acting upon cables or rods such as are attached to airplane controls and the like.

The principal object of this invention is to provide a system which will measure only the tensileforce which the operator applies to the cable which is actuated, eliminating all other effects such as initial loads, temperature effects involving lengthening of the fuselage and the like.

- One object of the invention is to provide an apparatus which will give an indication at a remote point of the amount of tension applied to a cable.

Another object is to provide a system for measuring the tension applied to control cables, which is small, light, convenient and which provides its pistons.

hence the force measuring device in that cable arm or rod displaces additional liquid into the balanced actuator, thereby creating a shift of This results in movement of a crank to which a gear sector is rigidly attached. Angular motion of the gear sector causes rotation; through a multiplying gear, of a spool-type potentiometer, the voltage-output of which is varied from a central null position. The voltage output is transmitted to a. meter on the observers desk or cockpit and the same voltage impulse operates a recorder of the traveling-strip type. The re-, cording and metering circuit is conventional.

Referring now to the accompanying drawings:

Fig. 1 is a schematic representation of the system applied to the rudder of an airplane. The showing is, in general, planwise;

Fig. 2 is a plan view of the Weighing or force measuring device, the internal parts, such as the belt crank and link being shown in phantom;

Fig. 3 is a bottom view of a device shown in for the storage of xcess displaced hydraulic fluid. Fi 2;

Another object is to provide a system of the 4 IS a Sectmn taken on the line 44 of class described in which the result may be under Fl 2;

the continuous observation of an instructor at a point where the trainee is unable to observe it himself.

Other objects will be apparent to those skilled in the art upon reading the following specification.

The assembly of devices which this invention comprises is located as to its measuring or sensing elements in the cables or the rods which are attached to the element to be moved and which are in turn moved by or through some effort of th pilot or co-pilot in the navigation of the airplane. The sensing elements are in general tension-responsive force measuring devices in which pressure upon a metallic bellows is created by the tension of the cables or rods pulling on the devices from each end thereof. The force is transmitted by a bell crank and link to compress the bellows and to displace its internalcontained liquid to a balanced actuator. The liquid from the tension-responsive force measuring devic on one side enters one end of the balanced actuator or the liquid-from the other weighing deviceenters the opposite. end of the actuator. So long as there is no unbalanced load application-in the system, the pressures of the liquid oneach side of' the actuator counterbalance each other. When there is motion and an unbalanced application of load, as for example, whenthe, rudder is being shifted, there is more tension onone cable arm or rod than the other,

Fig.5 is a top view of a balanced differential pressure-responsive mechanism or actuator;

Fig. 6 is a bottom view of the same differential pressure-responsive mechanism or actuator, showing the exterior of the electrical equipment; and

Fig. '7 is a section taken along the line 1'| of Fig. 6 and shows the hydraulic channels of the actuator and the means for actuating the electrical system.

Referring again to Fig. 1, l0 and II are the left and right hand force responsive measuring devices which are connected in the joined cable arms I2 and I3, respectively of an airplane or facsimile thereof, of which I4 is the rudder or some other element of its aero-dynamic structure which is to be controlled by a pilot (not shown) who will operate the combination pedals and cranks I5 or I5a, or other control-initiating devices commonly found on airplanes. l6l6 are pulleys .over which the cable arms [2 and I3 are adapted to travel. I! and Ila are respectively the left hand and right hand hydraulic tubes leading from the force responsive measuring devices l0 and H to a balanced actuator l8 which is rigidly mounted on a base plate 6| which is attached to the airplane l9. A crank or lever 20 of the actuator is pivoted at fulcrum 2| and has rigidly attached to its inner end a gear sector 22, also adapted to pivot about the fulcrum 21.. Sector 22 engages a pinion 23 which is keyed to a larger multiplying gear 24 which in turn engages a pinion 25 keyed to a spool-type potentiometer 26. 21 are conductors leading from the potentiometer 25 to an indicator 28 which is in view of the test observer and to a recorder 29 which is a conventional element adapted to make a permanent record of the test upon a paper strip.

Referring now to the details of the devices [0 or H shown in Figs. 2, Band 4, 30 and 3| are strong side plates, one leg or side 32 being slightly longer than the corresponding side or leg 33. A bridge 34 connects the two legs, thereby defining a central oblong. opening. 35; Two smaller openings 36 and 31 the latter .in a bell.

crank 38 and the former through the side plates, serve for the attachment of cable ends to the device. Opening 31 extends transversely through the bell crank 38 at such a point that the open-.

ing 35 will be in line with it and the longitudinaliaxis of the 1 force (responsive device during the greater part of the m vemen un er one by theg-b'ell; crank- The bell crank 38 and a spacer Slat theloppositeend of the device are secured between theside plates 30 andp3l, the first by pivot=4l andthe second by bolts 40. The outer end of thelbell crank 38' is flattenedso as to nga an adiustablenstop, 42 which extends through a .spaoer w 43 and which. may be locked inedesiredposition by aanutflfl. The stop 42 prevents excessive shell crankmovement and too greatra; displacement ,ofhydraulic fluid from the bellows 52..

Ami-vet. or.;crank pin-- 55 is, provided in the other arm .of the,bell crank 38.;fort'he purpose of accommodatingalink 46,-,the lower, nd of which is pivotably attachedltoa centrally pivoted lever 48 and by .apivot. pin .41 The level-4.48 is pivotedat its middle point by aipivot 49 extendingbetween the side=plates-35and-13].; Its outer vendzis piv-, otedby pivot50ltoa .lug 5|.-.atta,ched to a hydraulic bellows 52, located in the free space or. opening 135.1 Theside-plates MIN-rand 31 are provided with enlarged openings permitting mov e-. mento-fthepivots 45, 41: and 50.; In order :that bellows .52 maylhaveequally distributed pressure oncitssendsand to..protect.them, (seeFigle). a lower plate 53 and anzuppcr plate 54 are provided. The lower.-p1ate53 carries thedouble lug, 5| .and

the upper plate 54 is held by the rear spacer:;39

to which it-maybe weldeds 56is a spacer bar through'which and through the'plates 30 and 3! extend bolts 51 Upper plate 54 "is providedwith bosses 58 and 59, the first of -these having. a threaded. opening .60 :forp-the reception of the hydrauliopipe l'l.t

Tension: on the .device. [0 "or :I l between. openings 36 and .3!- causesthe bell crank 38 to pivot on boltg 4|, thereby forcing down pivot 45 and nk;,46 heright; hand endof ,the bellowsactuatinglever 48 ,is thereby depressed, pivoting leverabout pivot 49 and compressing .the, bellows 52. Hydrauliofluid from the bellows is then forced'through the pipe I! orv i la to the balancing actuat0r;;l8. The stop 42 .will prevent thebell- 4 Fig. l. Hydraulic access to the manifold 63 is obtained through the opening 64 and access to the right hand manifold 62 is obtained through opening 55. Extending between the manifolds nearest the top plate S Lthere is anextensible storage reservoir assembly generally indicated at M which comprises a metallic bellows 61 which is in hydraulic communication with the manifold 62. Bolted through this manifold there is a sleeve 53in which-a smooth stem 69 is held stationary. Sleeve 68 is surrounded by a heavy coil spring is, having a compressive strength greater than the normal; load on the system. The outer end of spring ll abuts a buffer ii so as to exert sufilcient pressure against it to collapse the bellows El when-the latter is empty. The stem 69 extends through the buffer piece ll and may be seen in Fig. '7. The bellows E1 is closed at that end which is adjacent the buffer H by a wall upon which there is a boss i2gwhich is adapted to centerthe bellows -in,:-th :bore .13 of. the buffer J l and toeontacttheohter end of the stem BQ When; the bellows 67 isfully-extended. Hydrauliczfluid:

is supplied to manifold :62;;through-the :tube l'l andopening ;whi le ,tube Haesuppl-ies manifold 63 through opening. 64.1 66 ista duplicate storage reservoir, assembly except-= that it-is r81.

reversal. from left "to right, of theqelcmentsrfi'l, it, e9, 16 and fit lwhich make up; thestorage reef: ervoir assemblyrlk Openin :65.-serves-:as1s,em:.-, lc-ly 14 for access of hydraul fiqrfiuid While opens ing' $4 serves the assembly 56.1.

Fig. 6 presents the base :plate 61 in z reversed position, since Fig. 6 is a view upward from .bee: low while-Fig. 5.is.a, .viewdronr above..- In Fig; 6 bellows l5, which-alsocappears in -Fi-g.'.7,5is seen from. below. and is shown: to :be mounted between:

the manifolds 63 and 62. The remaindenzofthe balancing mechanism which is; indicatedinFig. 7 by T8 does not appear in. Fig; .6 because it.;is2:hid= den by various mechanical and electricalliparts shown inFig. 7 as follows; .25 is thespooletype potentiometer previously referred.--to,the electrical connections 18. and 19 and .80.;arev-led $05.3 receptacle :8 I; into whichthe :conduit 21: is plugged; Actuatably connected. :to thespotentiometer 1 26; there is the pinion 25, the large multiplyingigea'r. 24 meshing withsamelthepinion 23 and the gear sector :22 attached to.the crank ordever 205 A supporting block 7"! is adjustably mountediion the :baseplate =6| 'upon whichE-the crankLZBand gear sector 22 are-pivoted at 2 l By :varyingthe position-of the'block' ll the-lower fulcrum 'point of the lever 20 can be varied to-control the mesh ing relation between thete'eth of. sector 22 and the teeth'of pinion 23.: Likewise. a mountingplate' 85 is provided for the-pinion-23 iand the-large multiplying gear 24, this plate may-also'h'ave a slightly 1 variable position. to. controlxthe. degree of mesh betweenthegear 24'and.pinion 25; 1

The outer endof the crank'or 16V6f20 is piv totally: connected late 8.6..to a spool: 81 i which crank from being actuated. to. such adegree as V is interposed between the hydraulic bellows .15 and alsecond. hydraulic. bellows B8,. The-spool 81 is provided with: an: upwardly projectingpost 83 whichcanbe seen 'in'Fig. 6,- and:which:'ser-ves to limit. the travel of spool 81 movement ofpost 89 being limited-g between two stops 96.;andi9t, which are attached "to atop plate-84. The -ad justed position oft-he block' 'il may itself be-regulated 'by a screwadj ustment 92- :in ablock ou the base-Btlshown: in Figl- 6 in engagement with adjustable block 1 The hydraulic bellows '88 is :actuated byhy- .draulic fiuid entc'ring a channel 93 in manifold "w re F62 and through the sleeves 9a and 9a anchored therein from whence departs a channel 91 through the storage reservoir assembly 14 to bel- .flowing in through the opening 65 into the channel 93 and thence into the channel 95 to fill the 'bellows 88 and shift the spool 81 to' the left. Whichever force is greater will move the spool 81 'in its directionin'a degree substantially proportional to the differential pressure and shift the lever to rotate the pinion andmultiplying gear 24 in a direction contrary to the application of the force. However, pinion 25 in potentiometer 26 will rotate in the same direction as the controlling force.

Should the pressure upon the bellows 52 and device Hl or H be so great that danger of rupturing the bellows 15 or 88 would be imminent, the excess from pipe I1 runs through channel 93 into bellows 6'! and thereby pushing against the buffer H. This action overcomes the pressure of the heavy coil spring 10 and expands the bellows 61, thereby providing more space to accommodate the excess fluid. Excess fluid from pipe lla will run through the hydraulic channel 96 in the manifold 63 and thence through a channel in assembly 66 in Fig. 5 corresponding to the channe1 94 in the assembly generally indicated at 14 in Fig. 7, thereby performing the same series of movements and leading to the same results as shown in assembly 14, but in an opposite direction. If the tension on the cable arms l2 and I3 is great enough to force the spool 81 in one direction to such an extent as to force almost all of the hydraulic fluid out of one or the other bellows 15 or 88, fill the corresponding reservoir assembly completely and still exert a high degree of pressure, then the post 89 on spool 81 will come into contact with one of the stops 90 or 9|, beyond which it cannot go; therefore the system will lock solidly against one or the other of the stops. Up to that point however, it is evident that the coil spring Ill will follow Hookes law and will apply a degree of pressure to the excess fluid which is, at a given instant, inversely proportional to the length of the spring.

Between the extremes of contact limits of the post 89 with either stop 98 or 9|, the voltage output from the potentiometer 26 through the conventional electric circuit (not shown in detail) will move the hand on the indicator 28 and the needle of the recorder 29 to furnish the desired indications and records indicative of the difference in the tensions exerted on the cable arms l2 or [3. These arms are not meant to be operator-actuated both at one time. Direction of departure of the hand or needle from the middle null point on the indicator or recorder will give the indication as to which arm is being tensioned and the amount of the applied tension.

Occasionally it will be unavoidable that both cable arms l2 and I3 are tensioned by forces beyond the control of the operator. One such a case occurs when thermal expansion of the fuselage takes place due to the heating effect of sunlight or other cause. Both unintended tensions if equal, cancel each other in this system be- 7 cause they oppose each other in the balanced actuator I8; If the forces are unequal, only the difference will be registered on the indicator "28 or recorder 29, because the spool 87 of actuator l8 willbe shifted toleft or right'in proportion to the difference between the forces. The electrical system will, of course, indicate only the shift of the spool 81, not the absolute pressure upon it. Whatwe claim is:

1. In a force measuring system, a pair of force responsive devices each including a hydraulic bellows and means responsive to cable tension for putting pressure on said bellows to force hydraulic fluid therefrom, a cable attached to each end of said force responsive devices, hydraulic tubes adapted-to carry fluid away from said bellows, a hydraulic balanced actuator, connections at each'end of said actuator receiving the outer ends of said hydraulic tubes, a central movable spool, hydraulic bellows on each side of said spool, manifolds connected to said bellows for conveying fluid to and from said bellows, a lever pivoted to said spool and to a fulcrum outside the actuator, a potentiometer, means connected to said lever for driving said potentiometer in response to oscillatory movement of said spool and an electric circuit including said potentiometer and a null instrument for indicating the difierential magnitude and direction of tension on the force responsive devices as applied by the cable.

2. A system according to claim 1 having in addition a reservoir for the reception of excess hydraulic fluid from said actuator, and'spring means on said reservoir for applying a pressure on said excess fluid, which pressure is at any given instant inversely proportional to the length of said spring.

3. In a differential system for measuring the tensional force applied by an operator to one or the other end of a joined cable, a pair of force transmitting devices connected in said cable at corresponding points, said devices including hydraulic bellows and hydraulic fluid within said bellows and means for applying force to said fluid in proportion to the pull exerted on the cable, a balanced hydraulic actuator hydraulically connected between the said devices to receive an equal amount of hydraulic fluid from each of said devices when the tension upon them is equal, a spool included in said actuator, the position of which is laterally shiftable in response to the excess of fluid entering one side of the actuator over that which is contained in the other side, levermeans attached to said spool, said means being rockable by the displacement thereof, a potentiometer, driving means for said potentiometer, said means being actuable by the rocking motion of said lever, and indicating means showing the extent and direction of the driven motion of said potentiometer.

4. In a force responsive device adapted to indicate cable tension, a dual substantially U- shaped frame having a substantially central crosswise opening and an end crosswise opening, a bell crank pivoted at the end of one leg thereof, said bell crank having an opening for the connection of a cable thereto, a first pivoted link extending athwart said frame in operative contact with said bell crank, a lever pivoted at substantially its mid point and extending along a leg of said frame a pivot joining the first link and the lever at one end, a hydraulic bellows mounted within said opening and adapted to be engaged and compressed endwise by a free end of said lever upon the cable being subjected to tension through-said openingy-inlsaidt bell tcrank, ;and-=-:-a..-.hydrau1ic tubeapositioned with. .itsiend substantially: in said framel in fluid communication with said bellows tovreceivehydraiil-iofiuid therefrom when the .bellows vis ll heavily compressed, all -of-said :parts excebts'ubstaritially -said bellows: (and said pivotsbeing mounted .s'ubstantially within said frame.

5. A hydraulic actuator responsive to.difierenitialvpressure comprising-the combination of a @pairof spaced manifolds, hydraulic tubes.c0n

-sleeve being connected to a respeotiveman'ifold -..to proj ecti inwardly in axialalignment with the 'othemsleeve, a hydrauliol bellows .vattachedfltolthe iii vand a potentiometer driven 'bysaid V geartrain.

WILLIAM W. WOOD, JR.

LESTER 'E; LUNDQUIST, JR.

iReferenoes Gited:;in gthevl'file 1 of i this patent UNITED STATES PATENTS Number Name Date 1,417,462 Eason May 23, 1922 1,543,061 .Danielson. 1Jun 23,1 1925 1,568,140 zEdgewetal. Jan.u,5,',1926 1,783,251 Marret a1. Dec. 2, 1930 ;1,949,908 Hawko Mar. 6, 11934 -t.2,235,279 Bunker Mar. 18,1941 2,505,070 Shaw. Apr. 25;.1950 

